Current trends in the manufacture of electronic devices require semiconductors to be fabricated on smaller scales without sacrificing performance or capabilities. Inspecting or measuring semiconductor wafer attributes during the fabrication process may be preferred because an electronic system or device may not function properly if it includes a semiconductor that has not been fabricated within sometimes delicate specifications. Therefore, several optical metrology techniques may be utilized to measure spatial and/or physical attributes of semiconductor wafers at various stages in the fabrication process to ensure proper performance of a finished product.
For example, certain applications require tight control of thickness and active carrier concentration of doped semiconductor layers, such as P-doped, N-doped layers and the like. Accordingly, it may be necessary to extract information about both thickness and active carrier concentration of a doped layer of a semiconductor wafer at various stages of the semiconductor fabrication process. In addition, nondestructive measurement techniques may be necessary to ensure the semiconductor wafer does not sustain damage causing the fabricated semiconductor to function improperly.
Commercially suitable technologies are not yet available for simultaneously extracting thickness and active carrier concentration from reflectance signals without one of thickness or active carrier concentration being known. Several current technologies, such as those disclosed in Clarysse et al., J. Vac. Sci. Technol. B24(3) 1139 (2006), Bogdanowicz et al., J. Vac. Sci. Technol. B26(1) 310 (2008), and Bogdanowicz et al., J. Applied Phys. 108, 104908 (2010), require unduly complicated modeling and excessive data processing. Other methods of measurement, such as secondary ion mass spectroscopy (SIMS) or scanning spreading resistance microscopy (SSRM), may cause destructive interaction with the semiconductor wafer. Thus, they are also inappropriate measurement techniques for wafers destined for semiconductor fabrication.